Lithography system and operation method thereof

ABSTRACT

A method including steps as follows is provided. A primary droplet and a satellite droplet are shot toward an excitation zone. The satellite droplet is deflected away from the excitation zone. A laser beam is emitted toward the excitation zone to excite the primary droplet to generate an extreme ultraviolet (EUV) light. The EUV light is directed onto a reticle using a first optical reflector, such that the EUV light is imparted with a pattern of the reticle. The EUV light with the pattern is directed onto a wafer using a second optical reflector.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims priority to U.S. Provisional Application Ser.No. 62/718,936, filed Aug. 14, 2018, which is herein incorporated byreference.

BACKGROUND

Manufacturing of an integrated circuit (IC) has been driven byincreasing the density of the IC formed in a semiconductor device. Thisis accomplished by implementing more aggressive design rules to allow alarger density of the IC device to be formed. Nonetheless, the increaseddensity of IC devices, such as transistors, has also increased thecomplexity of processing semiconductor devices with decreased featuresizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a lithography system according to some embodiments ofthe present disclosure.

FIG. 2 is a flow chart of a process according to some embodiments of thepresent disclosure.

FIG. 3 illustrates the lithography system of FIG. 1 with which theprocess of FIG. 2 is implemented according to some embodiments of thepresent disclosure.

FIG. 4 illustrates a drawing of partial enlargement of the lithographysystem of FIG. 3.

FIG. 5 illustrates the lithography system of FIG. 1 with which theprocess of FIG. 2 is implemented according to some embodiments of thepresent disclosure.

FIG. 6 illustrates a lithography system according to some embodiments ofthe present disclosure.

FIG. 7 illustrates a drawing of partial enlargement of the lithographysystem during operation.

FIG. 8 illustrates a drawing of partial enlargement of a lithographysystem during operation according to some embodiments of the presentdisclosure.

FIG. 9 illustrates a drawing of partial enlargement of a lithographysystem during operation according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Furthermore, spatially relative terms, such as “beneath,” “below,”“lower,” “above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The advanced lithography process, method, and materials described in thecurrent disclosure can be used in many applications, including fin-typefield effect transistors (FinFETs). For example, the fins may bepatterned to produce a relatively close spacing between features, forwhich the above disclosure is well suited. In addition, spacers used informing fins of FinFETs can be processed according to the abovedisclosure.

FIG. 1 illustrates a lithography system 100A according to someembodiments of the present disclosure. The lithography system 100Aincludes a chamber 102, a collector 110, a laser generator 120, adroplet generator 130, a droplet catcher 135, an inlet port 140, anoutlet port 142, optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168, a reticle 170, a droplet deflector 180, and controllers 190,191 and 192. The lithography system 100A is an extreme ultraviolet (EUV)exposure tool that can perform an exposure operation for exposing aphotoresist layer 302 coated on a wafer 300 within the chamber 102. Forexample, the lithography system 100A may include a stepper 104 disposedwithin the chamber 102, and the wafer 300 on which the photoresist layer302 is coated is mounted on the stepper 104. The stepper 104 is movablein the chamber 102 and is configured to shift the wafer 300, such thatthe wafer 300 can be shifted at a suitable position for the exposing.

The collector 110 is disposed within the chamber 102. In someembodiments, the collector 110 is mounted to a support (not shown inFIG. 1) that is a part of the lithography system 100A. The collector 110has a concave mirror surface 112. The concave mirror surface 112 ofcollector 110 may have a focal point 114 and an axis of symmetry 116which can serve as an optical axis of the collector 110. In greaterdetail, the axis of symmetry 116 of the collector 110 connects a center118 of the mirror surface 112 and the focal point 114.

In some embodiments, the mirror surface 112 of the collector 110 canalso be a multilayer reflector of any suitable structure andcomposition. The mirror surface 112 can include a distributed Braggreflector formed from alternating layers of a high index of refractionmaterial and a low index of refraction material. For example, thealternating layers can be Mo and Si or Mo and Be. In some embodiments,the mirror surface 112 includes more than 20 pairs of alternatinglayers. In some embodiments, the mirror surface 112 obtains areflectivity greater than 60%. In some embodiments, the uppermost layerof the mirror surface 112 can be protected from oxidation by a cappinglayer, such as a layer of Ru. In some embodiments, the mirror surface112 has an opening 113 through the center 118 of the mirror surface 112,and the opening 113 can be provided to allow passage of a light beampropagated from a back side of the collector 110.

The laser generator 120 is disposed within the chamber 102 and at theback side of the collector 110, and thus the mirror surface 112 of thecollector 110 faces away from the laser generator 120. The lasergenerator 120 is configured to provide a laser beam. The laser generator120 can be oriented such that the laser beam emitted from the lasergenerator 120 can go along the axis of symmetry 116 of the mirrorsurface 112. Stated differently, the laser generator 120 is orientedsuch that an optical path 121 of the laser generator 120 is the same asthe axis of symmetry 116 of the mirror surface 112. The laser generator120 is configured to generate a laser beam traveling along the opticalpath 121 of the laser generator 120 and aiming at an excitation zone 122in front of the mirror surface 112 of the collector 110. In someembodiments, the laser beam generated by the laser generator 120 isfocused on the excitation zone 122. In some embodiments, the excitationzone 122 may be between the center 118 and the focal point 114 of themirror surface 112. The laser generator 120 may emit a laser beam fromthe back side to a front side of the collector 110 through the opening113 of the collector 110. In some embodiments, the laser generator 120includes a laser source, such as a pulse carbon dioxide (CO2) lasersource.

The droplet generator 130 and the droplet catcher 135 are disposedwithin the chamber 102 and on two opposite sides of the collector 110(e.g., a left side and a right side of the collector 110). The dropletgenerator 130 is configured to provide droplets. The droplet generator130 can be oriented such that the droplets shot from the dropletgenerator 130 can go along a droplet path 131 (i.e. an initial path forthe droplets) through the excitation zone 122 (i.e., the position onwhich the laser beam generated by the laser generator 120 is focused on)in front of the mirror surface 112 of the collector 110. Stateddifferently, the droplet path 131 intersects with the axis of symmetry116 of the mirror surface 112 at the excitation zone 122. Furthermore,because the optical path 121 of the laser generator 120 is the same asthe axis of symmetry 116 of the mirror surface 112, the droplet path 131intersects with the optical path 121 of the laser generator 120 at theexcitation zone 122 as well. As shown in FIG. 1, when the dropletdeflector 180 is turned on, a rear segment 131 r of the droplet path 131will be non-parallel with a front segment 131 f of the droplet path 131.For example, the front segment 131 f of the droplet path 131 issubstantially linear and perpendicular to the outlet of the dropletgenerator 180, but the rear segment 131 r of the droplet path 131 isslightly tilted toward the collector 110 because droplets will bedeflected by the droplet deflector 180, which will be described ingreater detail below.

The droplet catcher 135 is configured to catch the droplets from thedroplet generator 130. In some embodiments, example materials shot fromthe droplet generator 130 may include tin or other suitable materialthat can be used to generate EUV. In some embodiments, the pulses of thelaser beam provided by the laser generator 120 and the dropletgenerating rate of the droplet generator 130 are controlled to besynchronized such that the droplets receive peak powers consistentlyfrom the laser pulses of the laser beam. In some embodiments, the lasergenerator 120 and the droplet generator 130 can be collectively operatedto generate EUV light, and therefore the laser generator 120 incombination with the droplet generator 130 can serve as an EUV lightsource.

The inlet port 140 and the outlet port 142 pass sidewalls of the chamber102 and are coupled to the inside of the chamber 102. In someembodiments, the inlet port 140 and the outlet port 142 are configuredto provide a continuous gas flow through the chamber 102 during theoperation of the lithography system 100A, so as to protect the collector110 from contaminations, such as tin particles (e.g., tin debris).

The optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 arewithin the chamber 102 and are mounted to respective supports (not shownin FIG. 1) that are parts of the lithography system 100A. The opticalreflectors 152, 154, 156 are optically coupled between the collector 110and the reticle 170, and the optical reflectors 158, 160, 162, 164, 166,168 are optically coupled between the reticle 170 and the photoresistlayer 302 on the wafer 300. The optical reflector 152 is opticallycoupled to the collector 110, and thus the mirror surface 112 of thecollector 110 can reflect a light beam to the optical reflector 152.Afterward, the light beam can be reflected from the optical reflector152 to the reticle 170 through reflection by the optical reflectors 154,156. The optical reflector 158 is optically coupled to the reticle 170,and thus the light beam can be reflected from the reticle 170 to theoptical reflector 158. Thereafter, the light beam can be reflected fromthe optical reflector 158 to the photoresist layer 302 throughreflection by the optical reflectors 160, 162, 164, 166, and 168.

In some embodiments, the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, 168 are mirrors which respectively have reflectionsurfaces. In some embodiments, the optical reflectors 152, 154, 156, 158can be multilayer structures that operate as distributed Braggsreflectors. The thickness of the layers can be optimized for each of theoptical reflectors 152, 154, 156, 158 with respect to wavelength andangle of an incident light beam. In some embodiments, a first group ofthe optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168includes at least one concave mirror, and a second group of the opticalreflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 includes at leastone convex mirror.

The reticle 170 can be used to impart the light beam with a patternthereof so as to create a pattern in the photoresist layer 302. It isnoted that the pattern imparted to the light beam may not exactlycorrespond to the desired pattern in the wafer, for example if thepattern includes phase-shifting features. Generally, the patternimparted to the light beam will correspond to a particular functionallayer in a device being created in the wafer, such as an integratedcircuit. In some embodiments, the reticle 170 may include a distributedBragg reflector. In some embodiments, the reticle 170 may include phaseshifting layers and/or absorber layers to define the pattern. In someembodiments, the reticle 170 is an absorberless phase-shifting mask.

The droplet deflector 180 is disposed within the chamber 102, and thecollector 110 and the droplet deflector 180 are on two opposite sides ofthe droplet path 131 of the droplet generator 130 (e.g., an upward sideand a downward side of the droplet path 131 of the droplet generator130). In some embodiments, the droplet deflector 180 provides an airflowtoward the droplet path 131 to apply a force on the droplet path 131. Insome embodiments, the droplet deflector 180 applies sonic wave towardthe droplet path 131 to apply a force on the droplet path. For example,the droplet deflector 180 is a wave generator providing a wave, such as,a sound wave (e.g., vibrations in pressure, particle of displacement, orparticle propagation), a vibration wave, or combinations thereof. Thedroplet deflector 180 can be oriented such that the airflow or the waveprovided from the droplet deflector 180 can travel along a travelingpath 181 to a second position 182 in the droplet path 131 and betweenthe droplet generator 130 and the excitation zone 122. Stateddifferently, the traveling path 181 intersects with the droplet path 131of the droplet generator 130 at the second position 182, and thusprovides the airflow or the wave along the traveling path 181 to thesecond position 182.

The airflow or the wave provided by the droplet deflector 180 maydeflect at least one droplet in the traveling path 181. For example, insome embodiments, the droplet deflector 180 is a wave generator that canproduce high intensity sound waves traveling along the traveling path181, and droplets passing through the traveling path 181 may bedeflected by the pressure gradients of the high intensity sound waves.In some embodiments, the droplet deflector 180 can produce highintensity sound waves traveling along the traveling path 181 when thedroplet generator 130 shoots droplets along the droplet path 131, andthus the droplets at the second position 182 may be deflected by thepressure gradients of the high intensity sound waves, due to theintersection of the droplet path 131 and the traveling path 181. In someother embodiments, the droplet deflector 180 can supply an airflowtraveling along the traveling path 181 when the droplet generator 130shoots droplets along the droplet path 131, and thus the droplets at thesecond position 182 may be deflected by the pressure gradients of theairflow, due to the intersection of the droplet path 131 and thetraveling path 181.

The controller 190 is electrically connected the droplet generator 130and is configured to trigger the droplet shooting operation of thedroplet generator 130. In some embodiments, the controller 190 can beconfigured to halt the droplet shooting operation of the dropletgenerator 130. In some embodiments, after the droplet shooting operationof the droplet generator 130 is halted, the controller 190 can also beconfigured to resume the droplet shooting operation of the dropletgenerator 130.

The controller 191 is electrically connected the laser generator 120 andis configured to trigger the laser emission operation of the lasergenerator 120. In some embodiments, the controller 191 can be configuredto halt the laser emission operation of the laser generator 120. In someembodiments, after the laser emission operation of the laser generator120 is halted, the controller 191 can also be configured to resume thelaser emission operation of the laser generator 120.

The controller 192 is electrically connected to the droplet deflector180 and is configured to trigger the force applying operation of thedroplet deflector 180. In some embodiments, the controller 190 isconfigured to halt the force applying operation of the droplet deflector180. In some embodiments, after the force applying operation is halted,the controller 190 can be configured to resume the force applyingoperation of the droplet deflector 180.

In some embodiments, the controllers 190 and 192 can be programmed suchthat the controller 190 can trigger the droplet shooting operationbefore the controller 192 triggers the force applying operation. In someembodiments, the controllers 190 and 192 can be programmed such that thecontroller 190 can trigger the droplet shooting operation after thecontroller 192 triggers the force applying operation. In someembodiments, the controllers 190 and 192 can be programmed such that thecontroller 190 can halt the droplet shooting operation before thecontroller 192 halts the force applying operation.

In some embodiments, the controllers 190 and 191 can be programmed suchthat controller 190 can trigger the droplet shooting operation beforethe controller 191 triggers the laser emission operation. In someembodiments, the controllers 190 and 191 can be programmed such that thecontroller 190 can trigger the droplet shooting operation after thecontroller 191 triggers the laser emission operation. In someembodiments, the controllers 190 and 191 can be programmed such that thecontroller 190 can halt the droplet shooting operation before thecontroller 191 halts the laser emission operation.

In some embodiments, the laser emission operation, the droplet shootingoperation, and the force applying operation are synchronized. Forexample, the controllers 190, 191 and 192 can be programmed such thatthe controllers 190, 191 and 192 can synchronously trigger the dropletshooting operation, the laser emission operation, and the force applyingoperation.

FIG. 2 is a flow chart of a process 200 according to some embodiments ofthe present disclosure. FIG. 3 illustrate the lithography system 100A ofFIG. 1 with which the process 200 of FIG. 2 is implemented according tosome embodiments of the present disclosure. FIG. 4 illustrates a drawingof partial enlargement of the lithography system 100A of FIG. 3. Theprocess 200 includes actions S210, S220, S230, S240, S250, and S260. Thelithography system 100A can be operated to expose a photoresist layercoated on a wafer by the process 200. For example, as shown in FIG. 3,the wafer 300 on which the photoresist layer 302 is coated is mounted onthe stepper 104 within the chamber 102, and the lithography system 100Ais operated to expose the photoresist layer 302 coated on the wafer 300.

The action S210 is applying a force using the droplet deflector. Forexample, as shown in FIGS. 3 and 4, the controller 192 can trigger aforce applying operation such that the droplet deflector 180 can producea force along the traveling path 181 toward the second position 182. Insome embodiments, the force may be applied using a sound wave. In someembodiments, the sound wave has a frequency less than 20 Hz and thus canbe referred to as an infrasound wave. In some embodiments, the soundwave has a frequency greater than 20000 Hz and thus can be referred toas an ultrasound wave. In some embodiments, the droplet deflector 180can produce forces using other techniques, such as pressure wave,vibration wave, and/or electromagnetic wave.

The action S220 is generating a laser beam from a laser generator. Forexample, as shown in FIGS. 3 and 4, the controller 190 can be programmedto trigger a laser emission operation such that the laser generator 120can generate a laser beam 311. As previously described, the lasergenerator 120 can be oriented such that the laser beam 311 emitted fromthe laser generator 120 can go along the axis of symmetry 116 of themirror surface 112, and the laser generator 120 is configured togenerate the laser beam 311 aiming at the excitation zone 122 in frontof the mirror surface 112 of the collector 110. As such, the laser beam311 can be sent to the excitation zone 122 in the axis of symmetry 116of the mirror surface 112. In some embodiments, the laser beam 311generated by the laser generator 120 is propagated through the opening113 and focused in the excitation zone 122.

The action S230 is generating fuel droplets by a droplet generator. Forexample, as shown in FIGS. 3 and 4, the controller 190 can trigger adroplet shooting operation such that fuel droplets 312 (e.g., dropletsof molten tin) are generated by the droplet generator 130. In someembodiments, the fuel droplets 312 may include tin or other suitablematerials that can be used to generate EUV. The fuel droplets 312 aregenerated by the droplet generator 130 to form a stream of the fueldroplets 312 directed along the droplet path 131 and toward theexcitation zone 122.

Together with the fuel droplets 312 there may also be generated verysmall fuel fragments referred to as satellite droplets 314 that resultfrom incomplete coalescence of the primary fuel droplets 312, asillustrated in FIG. 4. By way of example, a fuel droplet may have adiameter of about 30-50 microns whereas a satellite droplet may have adiameter of 6-10 microns. The satellite droplets 314 may lead to anegative impact on the EUV generation. For example, if a satellitedroplet 314 and a neighboring fuel droplet 312 travel along anundeflected droplet path 131′ into the excitation zone 122 together, thelaser beam might excite the satellite droplet 314 and thus lead to ashock wave. This shock wave might accelerate the neighboring fueldroplet 312 to move away from the excitation zone 122, which in turnwould result in incomplete excitation of the fuel droplet 312.

However, in some embodiments of the present disclosure, because thedroplet deflector 180 applies a force along the traveling path 181 tothe second position 182 between the excitation zone 122 and the dropletgenerator 130, the fuel droplets 312 and the satellite droplets 314 canbe deflected from the undeflected path 131′. Moreover, because thesatellite droplets 314 have lighter weights than the fuel droplets 132,the satellite droplets 314 can be deflected by greater distances thanthat the fuel droplets 132 are deflected by. Therefore, the fueldroplets 312 and the deflected satellite droplets 314 will move alongdifferent paths P1 and P2. In greater detail, the path P1 along whichthe deflected fuel droplets 312 move intersects with the excitation zone122, but the path P2 along which the deflected satellite droplets 314move does not intersect with the excitation zone 122. Stateddifferently, the deflected fuel droplets 312 will pass through theexcitation zone 122, but the deflected satellite droplets 314 will notmove into the excitation zone 122. In this way, shock waves resultingfrom excitation of the satellite droplets 314 will be reduced, which inturn will prevent acceleration of the fuel droplets 312 in theexcitation zone 122 resulting from the shock waves, thus preventing thefuel droplets 312 from incomplete excitation. Moreover, due to absenceof accelerating the fuel droplets 312 by the shock waves, the fueldroplets 312 may pass through the excitation zone 122 at a substantiallyconstant speed.

In some embodiments, the droplets (e.g., the fuel droplets 312 and thesatellite droplets 314) are shot out by the droplet generator 130 afterturning on the droplet deflector 180, so that undeflected satellitedroplets 314 can be reduced. The asynchronous turn-on operations of thedroplet generator 130 and the droplet deflector 180 can be achieved bythe individual controllers 190 and 192. For example, the controller 190triggers the droplet shooting operation after the controller 192triggers the force applying operation.

In some embodiments, the droplet deflector 180 is turned off afterstopping shooting the droplets (e.g., the fuel droplets 312 and thesatellite droplets 314), so that undeflected satellite droplets 314 canbe reduced. The asynchronous turn-off operations of the dropletgenerator 130 and the droplet deflector 180 can be achieved by theindividual controllers 190 and 192. For example, the controller 190halts (i.e., stops) the droplet shooting operation before the controller192 halts (i.e., stops) the force applying operation.

The deflected fuel droplets 312 goes toward the excitation zone 122which is at the focus of the laser beam 311, so that the fuel droplets312 are vaporized by the laser beam 311 to form an EUV-generatingplasma. For example, when the laser beam 311 is incident on a fueldroplet 312T, the fuel droplet 312T can be excited, so as to producehigh-temperature plasma 316. In some embodiments, the high-temperatureplasma 316 may be referred to as a microplasma which can generate EUVlight 138, as shown in FIG. 3. In some embodiments, the lithographysystem 100A produces EUV light 138 with a wavelength in the range fromabout 3 nm to about 15 nm, for example a wavelength of about 13.5 nm.

In some embodiments, the laser beam 311 is emitted from the lasergenerator 120 before turning on the droplet generator 130, so that thefuel droplets 312 can be exited. The asynchronous turn-on operations ofthe droplet generator 130 and the laser generator 120 can be achieved bythe individual controllers 190 and 191. For example, the controller 190triggers the droplet shooting operation after the controller 191triggers the laser emission operation.

In some embodiments, the deflected fuel droplets 312 moving along thepath P1 may be caught by the droplet catcher 135, and the deflectionsatellite droplets 314 moving along the path P2 may be caught by anotherdroplet catcher 136 which is separated from the droplet catcher 135. Thedroplet catcher 135 is misaligned with the droplet generator 130 forcatching the deflected primary droplets 312. In some embodiments, thecollector 110 is located between the droplet catchers 135 and 136. Forexample, the satellite droplet catcher 136 is disposed behind thecollector 110, because the satellite droplets 314 are deflected toward aback side of the collector 110. On the other hand, the fuel dropletcatcher 135 is disposed in front of the collector 110, because the fueldroplets 312 still move in front of the collector 110 even if they aredeflected by the droplet deflector 180.

In some embodiments, a vertical distance D1 between an outlet of thedroplet generator 130 and an entrance of the droplet catcher 135 is afirst distance D1, and a vertical distance D2 between the outlet of thedroplet generator 130 and an entrance of the minor droplet catcher 136is a second distance D2 greater than the first distance D1. Either thefirst distance D1 or second distance D2 is less than or equal to about30 cm (e.g., in a range from about 20 cm to about 30 cm). The first andsecond distances D1 and D2 are associated with deflections of the fueldroplets 312 and the satellite droplets 314. For example, the fueldroplets 312 may have a diameter in a range from about 25 μm to about 33μm and a mass in a range from about 7*10⁻¹² kg to about 8*10⁻¹² kg, andthe satellite droplets 314 may have a diameter in a range from about 5μm to about 7 μm and a mass in a range from about 2*10⁻¹³ kg to about3*10⁻¹³ kg. In such example, The droplet deflector 180 applies a force310 along the direction A1 to the satellite droplets 314 in a range fromabout 2.5*10⁻¹¹ N to about 3*10-11 N, such that the satellite droplets314 may be deflected by a desired second distance D2 (e.g., about 30cm), and the fuel droplets 312 may be deflected by a desired firstdistance D1 (e.g., about 25 cm). Applying the force 310 may includegenerating a wave or an airflow along the direction A1.

After generating the EUV light 138 by exciting the fuel droplets 312,the EUV light 138 is reflected by the mirror surface 112 of thecollector 110 toward the optical reflector 152, as shown in FIG. 3. Insome embodiments, the EUV light 138 is widely scattered to produce thereflected EUV light. The collector 110 can gather the EUV light 138 anddirect the EUV light 138 onto the optical reflector 152. The EUV light138 then can be reflected by the optical reflectors 152, 154, 156 insequence and to the reticle 170 as illustrated in FIG. 3. The reticle170 reflects the EUV light 138, which in turn imparts the EUV light 138with a pattern.

After using the optical reflectors 152, 154, 156 to reflect the EUVlight 138 to the reticle 170, a pattern is imparted to the EUV light138. Thereafter, the EUV light 138 imparted with the pattern is directedto the photoresist layer 302 coated on the wafer 300 by the opticalreflectors 158, 160, 162, 164, 166, 168. The lithography system 100Athereby selectively exposes the photoresist layer 302 coated on thewafer 300 in the pattern defined by the reticle 170 (i.e., the patternimparted to the EUV light 138).

The action S240 is providing a continuous gas flow through a chamber.For example, as shown in FIG. 3, a gas flow including gases 320A, 320B,320C, and 320D is provided to flow through the chamber 102. The gas 320Ais the gas flow as it enters the chamber 102 through the inlet port 140.The gas 320B is the gas flow when it resides within the chamber 102. Thegas 320C is a portion of the gas flow that is located in proximity tothe mirror surface 112 of the collector 110. The gas 320D is gas flow asit leaves the chamber 102 through outlet port 142. In some embodiments,the continuous gas flow is provided to flow through the chamber 102 inwhich the collector 110 and other components of the lithography system100A are enclosed. In some embodiments, concentration of contaminants inthe gas 320B can be reduced and the proportion of contaminants carriedaway with the outflow gas 320D can be increased by raising the flow rateof the gas flow through the chamber 102.

Following the actions S210, S220, S230, and S240, the process 200continues with the action S250 which is halting generating the laserbeam and generating the fuel droplets. For example, as shown in FIG. 5,which illustrates the lithography system 100A of FIG. 1 with which theprocess 200 of FIG. 2 is implemented according to some embodiments ofthe present disclosure, the controllers 190 and 191 can be programmed tohalt the droplet shooting operation and the laser emission operation,and thus halting the generation of the EUV light. In some embodiments,the controllers 190, 191 and 192 are programmed such that the laseremission operation and the droplet shooting operation are halted beforehalting the force applying operation, so as to reduce variation in theEUV light. After halting the laser emission operation and the dropletshooting operation, the process 200 continues with the action S260 whichis halting the force. For example, the controller 192 is programmed tohalt the force applying operation after halting the laser emissionoperation and the droplet shooting operation.

In the example configuration in FIG. 5, halting the force applyingoperation is performed after halting the laser emission operation andthe droplet shooting operation, but is not limited thereto. In otherembodiments, the force applying operation is halted before halting thelaser emission operation and the droplet shooting operation.

After halting the laser emission operation and the droplet shootingoperation, the controllers 190 and 191 can be programmed to resume thelaser emission operation and the droplet shooting operation. Similarly,after halting the force applying operation, the controller 192 can beprogrammed to resume the force applying operation. In some embodiments,after halting the laser emission operation, the droplet shootingoperation, and the force applying operation, the laser emissionoperation and the droplet shooting operation are resumed. The forceapplying operation can be resumed after resuming the laser emissionoperation and the droplet shooting operation. In some embodiments, afterhalting the laser emission operation and the droplet shooting operationand before halting the force applying operation, the laser emissionoperation and the droplet shooting operation can be resumed.

FIG. 6 illustrates a lithography system 100B according to someembodiments of the present disclosure. FIG. 7 illustrates a drawing ofpartial enlargement of the lithography system 100B during operation.Many aspects of the lithography system 100B are the same as or similarto those of the lithography system 100A as previously described inFIG. 1. For example, the lithography system 100B includes a chamber 102,a collector 110, a laser generator 120, a droplet generator 130, adroplet catcher 135, an inlet port 140, an outlet port 142, opticalreflectors 152, 154, 156, 158, 160, 162, 164, 166, 168, a reticle 170, adroplet deflector 180 a, and controllers 190, 192, and the detailedexplanation may be omitted. The lithography system 100B is an EUVexposure tool that can perform an exposure operation for exposing aphotoresist layer 302 coated on a wafer 300 within the chamber 102. Forexample, the lithography system 100B may include a stepper 104 disposedwithin the chamber 102, and the wafer 300 on which the photoresist layer302 is coated is mounted on the stepper 104. The stepper 104 is movablein the chamber 102 and is configured to shift the wafer 300, such thatthe wafer 300 can be shifted at a suitable position for the exposing.

Different from the lithography system 100A, the collector 110 and thedroplet deflector 180 a of the lithography system 100B are disposed onthe same side of a droplet path 131 of the droplet generator 130. Inthis way, the droplet deflector 180 a can apply a force along adirection A2 away from the collector, so as to deflect the satellitedroplets 314 away from the collector 110. As a result, the satellitedroplet catcher 136 a is disposed in front of the collector 110, so asto catch the deflected satellite droplets 314. In some embodiments, adistance between the droplet catcher 136 a and the collector 110 along adirection parallel to the axis of symmetry 116 of the collector 110 isgreater than a distance between the excitation zone 122 and thecollector 110 along the direction.

FIG. 8 illustrates a drawing of partial enlargement of a lithographysystem 100C during operation according to some embodiments of thepresent disclosure. Many aspects of the lithography system 100C are thesame as or similar to those of the lithography system 100A as previouslydescribed in FIG. 1. For example, the lithography system 100C includes acollector 110, a laser generator 120, a droplet generator 130, a dropletcatcher 135, a droplet deflector 194, and controllers 190, 192, and thedetailed explanation may be omitted. The lithography system 100C is anEUV exposure tool that can perform an exposure operation, as previouslydescribed.

Different from the lithography system 100A, the droplet deflector 194can generate an electric field on the droplet path 131, so as to deflectthe fuel droplets 312 and the satellite droplets 314 from theundeflected path 131′ by a force resulted from an electric field, suchas Coulomb force. In order to generate an electric field, the dropletdeflector 194 may include a pair of electrode plates 196A and 196B whichare disposed at opposite sides of the droplet path 131. When a voltagedifference is applied to the electrode plates 196A and 196B, an electricfield in a direction substantially perpendicular to the droplet path 131can be generated. For example, a positive voltage is applied to theelectrode plate 196A and a negative voltage is applied to the electrodeplate 196B, which in turn generates an electric field in a downwarddirection A3, such that the fuel droplets 312 and the satellite droplets314 in the electric field can be deflected by a force 310 along thedownward direction A3. In this way, as previously described, since thedroplet deflector 194 can apply the force 310 along the downwarddirection A3, it makes the deflected fuel droplets 312 pass through theexcitation zone 122 but make the deflected satellite droplets 314 notmove into the excitation zone 122.

In some embodiments, the controller 192 electrically connected to thedroplet deflector 194 is configured to adjust a voltage differenceapplied into the electrode plates 196A and 196B, so as to vary anintensity of an electric field generated by the electrode plates 196Aand 196B. In some embodiments, the electrode plates 196A and 196B aresymmetric about the droplet path 131. In other embodiments, theelectrode plates 196A and 196B are asymmetric about the droplet path131. For example, the electrode plate 196B may be further away from thedroplet path 131 than the electrode plate 196A, so as to avoid the fueldroplets 312 and the satellite droplets 314 from hitting the electrodeplate 196B.

FIG. 9 illustrates a drawing of partial enlargement of a lithographysystem 100D during operation according to some embodiments of thepresent disclosure. Many aspects of the lithography system 100D are thesame as or similar to those of the lithography system 100C as previouslydescribed in FIG. 8. For example, the lithography system 100D includes acollector 110, a laser generator 120, a droplet generator 130, a dropletcatcher 135, a droplet deflector 194 a, and controllers 190, 192, andthe detailed explanation may be omitted. The lithography system 100D isan EUV exposure tool that can perform an exposure operation, aspreviously described.

Different from the lithography system 100C, a voltage difference appliedinto the electrode plates 196A and 196B of the droplet deflector 194 ais inverse to the voltage difference applied into the electrode plates196A and 196B of the droplet deflector 194 as previously described inFIG. 8, and therefore the droplet deflector 194 a can deflect the fueldroplets 312 and the satellite droplets 314 from the undeflected path131′ by a force 310 along an upward direction A4. For example, anegative voltage is applied to the electrode plate 196A and a positivevoltage is applied to the electrode plate 196B, which in turn generatesan electric field in the upward direction A4, such that the fueldroplets 312 and the satellite droplets 314 in the electric field can bedeflected by the force 310 along the downward direction A4. In this way,since the droplet deflector 194 a can apply the force 310 along thedirection A4 away from the collector 110, it can deflect the satellitedroplets 314 away from the collector 110. In some embodiments, theelectrode plates 196A and 196B are symmetric about the droplet path 131.In other embodiments, the electrode plates 196A and 196B are asymmetricabout the droplet path 131. For example, the electrode plate 196A may befurther away from the droplet path 131 than the electrode plate 196B, soas to avoid the fuel droplets 312 and the satellite droplets 314 fromhitting the electrode plate 196A.

Based on the above discussions, it can be seen that the presentdisclosure offers advantages. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantage isrequired for all embodiments. One advantage is that the satellitedroplets can be deflected away from the excitation zone, which in turnwill reduce shock waves resulting from excitation of the satellitedroplets, which in turn will prevent acceleration of the fuel dropletsin the excitation zone, thus preventing the fuel droplets fromincomplete excitation.

According to various embodiments of the present disclosure, a method isprovided. The method includes steps as follows. A primary droplet and asatellite droplet are shot toward an excitation zone. The satellitedroplet is deflected away from the excitation zone. A laser beam isemitted toward the excitation zone to excite the primary droplet togenerate an extreme ultraviolet (EUV) light. The EUV light is directedonto a reticle using a first optical reflector, such that the EUV lightis imparted with a pattern of the reticle. The EUV light with thepattern is directed onto a wafer using a second optical reflector.

According to various embodiments of the present disclosure, a method isprovided. The method includes steps as follows. A first droplet and asecond droplet are shot along a same initial path, and the seconddroplet has a lighter weight than the first droplet. A force is appliedon the first and second droplets, such that the first and seconddroplets respectively move along a first path and a second pathdifferent the first path. A laser beam is emitted to the first dropleton the first path to generate an extreme ultraviolet (EUV) light. TheEUV light is directed onto a reticle using a first optical reflector,such that the EUV light is imparted with a pattern of the reticle. TheEUV light with the pattern is directed onto a wafer using a secondoptical reflector.

According to various embodiments of the present disclosure, alithography system includes a collector, a laser generator, a dropletgenerator, and a droplet deflector. The collector has a mirror surface.The laser generator aims at an excitation zone in front of the mirrorsurface of the collector. The droplet deflector is operative to apply aforce at a position between the droplet generator and the excitationzone.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: shooting a primary droplet and a satellite droplet toward an excitation zone; deflecting the satellite droplet away from the excitation zone; emitting a laser beam toward the excitation zone to excite the primary droplet to generate an extreme ultraviolet (EUV) light; directing the EUV light onto a reticle using a first optical reflector, such that the EUV light is imparted with a pattern of the reticle; and directing the EUV light with the pattern onto a wafer using a second optical reflector.
 2. The method of claim 1, wherein emitting the laser beam is performed such that the deflected satellite droplet is free from excited by the laser beam.
 3. The method of claim 1, wherein deflecting the satellite droplet is performed such that the primary droplet is deflected.
 4. The method of claim 3, wherein the primary droplet is deflected by a first distance, and the satellite droplet is deflected by a second distance greater than the first distance.
 5. The method of claim 1, wherein the primary droplet and the satellite droplet are shot out from a droplet generator along an initial path, and deflecting the satellite droplet comprises applying a force on the initial path.
 6. The method of claim 5, further comprising: halting shooting the primary droplet and the satellite droplet after applying the force; and halting applying the force after halting shooting the primary droplet and the satellite droplet.
 7. The method of claim 5, further comprising: halting emitting the laser beam before halting applying the force.
 8. The method of claim 5, wherein the laser beam is emitted along a direction opposite a direction of the force.
 9. The method of claim 5, wherein the laser beam is emitted along a direction the same as a direction of the force.
 10. The method of claim 1, wherein the laser beam is emitted from a back side of a collector to a front side of collector, and the satellite droplet is deflected toward the back side of the collector.
 11. The method of claim 1, wherein the laser beam is emitted from a back side of a collector to a front side of collector, the satellite droplet is deflected away from the front side of the collector.
 12. A method, comprising: shooting a first droplet and a second droplet along a same initial path, the second droplet having a lighter weight than the first droplet; applying a force on the first and second droplets, such that the first and second droplets respectively move along a first path and a second path different the first path; emitting a laser beam to the first droplet on the first path to generate an extreme ultraviolet (EUV) light; directing the EUV light onto a reticle using a first optical reflector, such that the EUV light is imparted with a pattern of the reticle; and directing the EUV light with the pattern onto a wafer using a second optical reflector.
 13. The method of claim 12, wherein the second droplet is free from emitted by the laser beam during emitting the laser beam to the first droplet.
 14. The method of claim 12, further comprising: catching the first and second droplets using different droplet catchers, respectively.
 15. The method of claim 12, wherein applying the force on the first and second droplets comprises: generating a wave or an airflow to the first and second droplets.
 16. The method of claim 12, wherein applying the force on the first and second droplets: generating an electric field on the initial path of the first and second droplets.
 17. A lithography system, comprising: a collector having a mirror surface; a laser generator aiming at an excitation zone in front of the mirror surface of the collector; a droplet generator; and a droplet deflector operative to apply a force at a position between the droplet generator and the excitation zone.
 18. The lithography system of claim 17, further comprising: a droplet catcher, wherein the excitation zone is between the droplet generator and the droplet catcher, and the droplet catcher is misaligned with the droplet generator.
 19. The lithography system of claim 17, further comprising: a droplet catcher on a back side of the collector.
 20. The lithography system of claim 17, further comprising: a droplet catcher in front of the mirror surface of the collector, wherein a distance between the droplet catcher and the collector along a direction parallel to an optical axis of the collector is greater than a distance between the excitation zone and the collector along the direction. 